subpanel question -- grounding

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Old 07-30-15, 06:48 AM
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subpanel question -- grounding

I have 3 wires going to garage subpanel in rigid metal... the conduit has continuity between the main panel and the sub panel. There is no additional ground wire. The subpanel neutral bus bar is NOT bonded to sub panel box.

The main service has its own ground rod. The subpanel has a separate ground rod. The subpanel box is bonded to that ground rod with a ground bushing.

Is that correct? I probably left something out, so please ask away.
 
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Old 07-30-15, 07:30 AM
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All sounds ok if the sub is in a detached garage. If in an attached garage, the sub should not have its own ground rod. The sub will probably need an add-on ground bar screwed to the box if it doesn't already have one.
 
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Old 07-30-15, 07:36 AM
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yes I should have mentioned... its detached garage. And there is an additional ground bar that is mounted to the enclosure ... the only thing connected to it is the conductor to the ground rod. The individual circuit neutrals are attached to the neutral bus bar (that is NOT bonded to box).
 
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Old 07-30-15, 08:14 AM
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As long as the grounding conductotrs from the branch circuits in the garage are on the grounding bar it sounds good.
 
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Old 07-30-15, 09:39 AM
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There are no separate grounding conductors, its all piped in EMT.
 
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Old 07-30-15, 06:15 PM
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The EGC is the conduit, does that change anything?
 
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Old 07-30-15, 07:55 PM
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Please explain how you piped EMT to a detached garage. Is the pipe underground? Did you use rain tight fittings if above ground? Is the EMT run through a concentric/eccentric KO?
 
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Old 07-30-15, 08:22 PM
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I took it that the branch circuit was piped in EMT.
 
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Old 07-30-15, 08:36 PM
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It is not a branch circuit, it is a feeder to a sub panel.
 
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Old 07-31-15, 05:28 AM
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The feeder span the yard UNDERGROUND in 1" rigid metal conduit. The circuits in the enclosed garage are in 1/2" EMT and serve as the EGC. All the metal from the main panel to the garage circuits are bonded.

also, not related to the EGC inquiry....

there are 2 20 amp circuits in the garage/sub. The feeder is 3 wire #8. It was protected by a 40amp breaker in the main. I replaced the breakers in the main but did not have a 40... instead I used a 30 amp. I know that is ok from a safety standpoint, but if there was a fault, would the 30 amp now trip before either of the 2x20 amp in the sub?
 

Last edited by superjojo; 07-31-15 at 05:45 AM.
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Old 07-31-15, 08:26 AM
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The subpanel has a separate ground rod. The subpanel box is bonded to that ground rod with a ground bushing.
So, the GEC is in metallic conduit? If so, the GEC must be bonded to both ends of that conduit.
 
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Old 07-31-15, 08:40 AM
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There is no problem using the 30A breaker on the feeder.
 
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